the present invention relates to a filter press of the type hereinafter referred to as "of the type described" which comprises a plurality of plates each supporting a sheet of filter material, the plates being mounted in a row so that they can be arranged in a first, working, configuration wherein they are all clamped together and a second, cleaning, configuration wherein there is a gap between a selected two of the plates to allow removal of residue therefrom. The plates may be made of a rigid material such as ebonite, timber, cast iron or polypropylene with or without the incorporation of flexible membranes.
A known filter press of this type has a pair of parallel horizontal supports upon which rest lugs extending from opposite sides of the plates. Each plate is of cast iron and some four feet square by four inches thick. At one end the supports are attached to a fixed headstock having a liquid inlet and at the other end they are attached to a hydraulic ram assembly. In use the ram presses the plates tightly together and against the headstock. After filtration, the residue may, if desired, be washed and dried while within the plates pressed tightly together.
When it is necessary to remove residue from the plates the ram is withdrawn and the last plate, i.e. the plate remote from the headstock, is moved away from the remainder of the plates usually by a drive of some sort, and the residue is manually dislodged therefrom to fall into a collection vessel below the press. When the last plate is clean the next last plate is moved away from the remainder to a position close to the last plate and is itself cleaned. This process is repeated until all the plates are clean. The ram is then actuated to move all the plates simultaneously back to their working positions clamped against the headstock.
This known machine has two disadvantages. Firstly, the drive used to separate the plates for cleaning is such that a gap of one half to one inch-can be left between the plates as they are moved towards the ram. This means that whereas the gap between the last and next-to-last plates is quite long and makes for easy cleaning, the gap left between the first and second plates is much reduced and cleaning is more difficult. This has lead to the practice of separating the filter plates manually which is extremely laborious.
Secondly, and more seriously, the practice of using the ram to clamp all the plates simultaneously can result in very severe stresses being applied to the headstock and damage can be caused thereto.
This can happen whenever the plates in the pack are not parallel to the plane of the headstock as they advance towards it under the action of the ram. This discrepancy arises in various ways but can be observed and measured as it occurs in varying degree during the ram closure operation on presses of the type described where the plates can swing and are not positively held parallel to the headstock. Once the discrepancy has arisen the plates do not usually align themselves parallel to the headstock as the press closes because frictional forces prevent the sliding of the plates relative to each other.
Thus proper concentric compression with even distribution of force within the pack is prevented and this tends to promote leakage of process fluid during operation as well as distortion of the headstock and general structure of the press. In extreme cases the leakage is obvious and excessive and the eccentric loadings which arise can produce dangerous distortion of the structure of the press.